The invention concerns a method of preparing (4-alkylsulphonyl)-phenyl-2-(5H)-furanones, which are compounds inhibiting cyclooxygenase-2 (COX-2); as well as novel intermediate compounds useful for preparing these compounds.
(4-alkylsulphonyl)-phenyl-2-(5H)-furanone compounds useful as COX-2 inhibitors and their pharmacological applications as anti-inflammatories are known and described in the following documents: WO 97/44027, WO 97/28121, WO 98/41516, WO 96/19469, WO 97/16435 and WO 97/14691.
The synthesis of these compound involves a method in several steps involving an intermediary of the 4-alkylsulphonyl-xcex1-bromoisobutyrophenone type.
Thus WO 97/45420 describes a method of preparing (methyl-4-sulphonyl)-phenyl-2-(5H)-furanones from thioanisole involving five steps.
The second step of this method consists of brominating 4-thiomethyl-isobutyrophenone in order to obtain 4-thiomethyl-xcex1-bromoisobutyrophenone.
In the following step the 4-thiomethyl-xcex1-bromoisobutyrophenone is oxidised to 4-methylsulphonyl-xcex1-bromiosobutyrophene, which is a highly allergenic compound, and this compound is then esterified with a carboxylic acid in order to form a 2-methyl-1-(4xe2x80x2-methylsulphonylphenyl)-1-oxo-prop-2-yl ester.
This reaction is also accompanied by a certain number of by-products, including an elimination product, 4-(4xe2x80x2-methylsulphonylphenyl)-2-methyl-propenone.
The aim of the invention is to propose an alternative to the method described in WO 97/45420 and in particular a general method of preparing substituted (4-alkylsulphonylphenyl)2-(5H)-furanone compounds which avoids the problem posed by the xcex1-bromoisobutyrophenone-type intermediary, is easy to implement, avoids the formation of the elimination by-product and provides an acceptable yield of final product.
The work carried out by the inventors has now made it possible to propose a method meeting these expectations, and which in particular avoids passing through a toxic bromosulphone derivative and the formation of the aforementioned by-product.
The object of the invention is thus a method of preparing compounds of general formula I: 
in which
R1 is chosen amongst the groups
(a) OR5 where R5 represents a group chosen from amongst
(1) a C1-C6 branched linear or ring alkyl group;
(2) a mono-, di- or tri-substituted phenyl or naphthyl group in which the substituents are chosen from amongst:
hydrogen;
halogen;
(C1-C3) alkoxy;
CN;
(C1-C3) fluoroalkyl;
(C1-C3) alkyl;
COOH;
and
(b) mono-, di or tri-substituted phenyl in which the substituents are chosen from amongst:
hydrogen;
halogen;
(C1-C3) alkoxy;
CN;
(C1-C3) fluoroalkyl;
(C1-C3) alkyl;
COOH;
R2 represents a (C1-C6) alkyl group;
R3 and R4 represents independently of one another a hydrogen atom or a CHR6R7 group
in which R6 and R7 are independently of each other chosen from amongst:
hydrogen;
(C1-C10) alkyl;
(C1-C10) alkoxy;
OH;
CN;
CH2CN;
OCOR8;
(C1-C6) fluoroalkyl;
halogen;
CON (R8)2;
mono-, di or tri-substituted phenyl;
mono-, di or tri-substituted heteroaryl;
the substituents being chosen from amongst:
hydrogen;
halogen;
(C1-C6) alkyl;
(C1-C10) alkoxy;
CN;
CF3;
N3;
C (R9) (R10)xe2x80x94OH;
C (R9) (R10) xe2x80x94Oxe2x80x94(C1-C4) alkyl;
(C1-C6) fluoroalkyl;
R8 is chosen from amongst;
hydrogen;
(C1-C6) alkyl;
mono-, di- or tri-substituted phenyl, the substituents being chosen from amongst hydrogen, halogen, (C1-C6) alkyl, (C1-C6) alkoxy, (C1-C6) alkylthio, CN or CF3; and
mono-, di or tri-substituted benzyl, the substituents being chosen from amongst hydrogen, halogen, (C1-C6) alkyl, (C1-C6) alkoxy, (C1-C6) alkylthio, CN or CF3;
or two R8 groups from together with the nitrogen atom to which they are attached a ring with 5 to 7 atoms, and possibly comprising a heteroatom chosen from amongst O, S or NR9;
R9 and R10 are independently of one another chosen from amongst:
hydrogen; and
(C1-C10) alkyl; or
form, together with the atom to which they are attached, a ring with 3 to 7 carbon atoms and where applicable a nitrogen atom;
wherein it comprises the following steps:
a) reaction of a compound of general formula II: 
in which R2, R3 and R4 are as defined above and R12 represents a C1-C6 alkyl group,
with an acid of general formula III: 
in which R1 is as defined previously, in an anhydrous medium, in order to form a compound of formula IV: 
R1, R2, R3 and R4 being as defined above;
b) reaction of the compound of formula IV with a strong base in an aprotic solvent in order to obtain an intermediate ring compound of formula V: 
which, after elimination of a water molecule, forms a compound of general formula I; and
c) isolation of the compound of general formula I thus obtained.
The reaction of step a) takes place in an anhydrous solvent, preferably an ether, for example diethylether, or methyltertbutylether. The reaction temperature is advantageously between xe2x88x9220 and 40xc2x0 C. At the end of step a), a compound of general formula IV is obtained as well as secondary products in minor quantities. However, the aformentioned elimination product does not form.
For the reaction of step b), the strong base is advantageously chosen from amongst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN).
The elimination of a water molecule is achieved in a manner known per se, advantageously by thermal dehydration in the presence of a dehydration agent.
The dehydration agent can be chosen in particular from amongst trifuloroacetic acid esters, for example isopropyl trifluoroacetate, trichloracetic acid esters and alkyl or arylsulphonic acid esters.
The reaction preferably takes place in an aprotic solvent such as acetonitrile, N,N-dimethylformamide, N-methylsulphoxide, proprionitrile or nitromethane.
The dehydration is achieved by heating to reflux.
The molar ratio of the ester of formula IV to the strong base is generally between 1:1 and 1:2, a ratio of 1:1.5 being preferred.
The molar ratio of the ring ester of formula V to the dehydration agent is generally 1:1 to 1:2, a ratio of 1:1.2 being preferred.
The reaction is carried out at a temperature preferably between 0xc2x0 C. and the reflux temperature of the solvent.
Particularly advantageous reaction conditions are achieved by the use of a mixture of 1.2 equivalents of isopropyl trifluoroacetate and 1.5 equivalents of DBU in acetonitrile at reflux. Under these conditions, the reaction is terminated after 24 hours and the product crystallises by the addition of water after partial elimination of the acetonitrile. For more information, reference should be made to the description of the patent application WO 97/45420.
Step c) is carried out in a manner known per se, in particular by elimination of the solvent, precipitation of the product, recrystallisation, etc.
The epoxy compound of general formula II can be obtained by the reaction of a compound of general formula VI: 
in which R2, R3, R4 and R12 are as defined above, with an oxidising agent.
Oxidising agents can in particular include organic peracids, such as meta-chloroperbenzoic acid and peracetic acid or dioxiranes such as dimethyldioxirane, generated in situ or not. The reaction temperature is advantageously between xe2x88x9240xc2x0 C. and 30xc2x0 C.
The oxidising agent is used in excess with respect to the compound of general formula II (3 to 40 equivalents), so as to oxidise on the one hand the olefin function into epoxide and on the other hand the sulphide function into sulphone.
The compound of general formula VI can be obtained by reaction of a compound of general formula VII: 
in which R2, R3 and R4 are as defined above, with an alcohol of general formula VIII:
HO R12 xe2x80x83xe2x80x83(VIII)
R12 being as defined above, in the presence of a catalytic quantity of acid and a dehydrating agent.
Advantageously, the acid is chosen from amongst the sulphonic acids, for example p-toluene sulphonic acid, or the mineral acids, for example hydrochloric acid. By way of dehydrating agent, C1-C6 alkyl orthoformiates are preferred.
The reaction is carried out in an excess of alcohol of general formula VIII, this serving as a reactive solvent.
In the compound of general formula VIII, R12 is advantageously a methyl group, the alcohol being methanol.
Another object of the invention is a method of preparing a compound of general formula I as defined above, wherein it comprises the following steps:
(1) reaction of a compound of general formula IX: 
in which R2 is as defined above, in a solvent which is inert in the presence of a Lewis acid with a compound of general formula X: 
in which X is a starting group, preferably a chlorine atom, in order to form a compound of general formula VII: 
in which R2, R3 and R4 are as defined previously,
(2) reaction of a compound of general formula VII with an alcohol of general formula VIII:
R12-OHxe2x80x83xe2x80x83(VIII)
in which R12 represents a (C1-C6) alkyl group in order to form a compound of general formula VI: 
in which R2, R3, R4 and R12 are as defined above,
(3) reaction of the compound of general formula VI with an oxidising agent in order to obtain a compound of general formula II: 
in which R2, R3, R4 and R12 are as defined previously;
(4) reaction of the compound of general formula II as defined at step (3)
with an acid of general formula III: 
in which R1 is as defined previously, in an anhydrous medium, in order to form a compound of formula IV: 
R1, R2, R3 and R4 being as defined above;
(5) reaction of the compound of formula IV with a strong base in an aprotic solvent in order to obtain an intermediate ring compound of formula V: 
which, after elimination of a water molecule, forms a compound of general formula I; and
(6) isolation of the compound of general formula I thus obtained.
For the reaction of step (1), the Lewis acid is advantageously chosen from amongst A1C13, FeC13, TiC14 and SnC14 without however being limited to these. The non-reactive solvents comprise halogenated and polyhalogenated hydrocarbons such as the mono- or dihalo(C1-C4)alkyls, for example dichloromethane; the aromatic solvents such as nitrobenzene or halogenated aromatic compounds, as well as branched linear or ring C6-C10 hydrocarbons comprising notably hexane, cyclohexane, methylcyclohexane or CS2. For this step, cyclohexane or dichlorobenzene can in particular be chosen. The molar ratio of the compound of general formula IX to the compound of general formula X is generally between 1:1.5 and 1.5:1, a ratio of 1:1 to 1:1.5 being preferred. The reaction is generally carried out with an excess of the compound of general formula X. Generally the molar ratio of the compound of general formula IX to the Lewis acid is between 1:1.5 and 1.5:1.
Preferably, the molar ratio of the compound of general formula IX to the Lewis acid is between 1:1 and 1:1.5. The reaction can advantageously be carried out in a temperature range of between 0 and 25xc2x0 C., preferably 5 and 15xc2x0 C. The reagents are set to react until the reaction is completed, which occurs after an interval of time ranging from 8 to 4 hours, generally 1 to 2 hours. The reaction is preferably carried out in a nitrogen atmosphere. Steps (2) to (6) are carried out under conditions as described previously.
The compounds of general formula IX and X are commercially available compounds or ones which can easily be prepared by a person skilled in the art using well known routine methods.
In a first embodiment of the method of the invention, R1 is an RO group, R being as defined previously for R5.
The compound of general formula I then becomes a compound of general formula Ia: 
The method according to the invention in this case comprises the following steps:
a) reaction of a compound of general formula II 
in which R2, R3 and R4 are as defined previously and R12 represents a C1-C6 alkyl group,
with an acid of general formula IIIa 
in which R is as defined above, in an anhydrous medium, in order to form a compound of general formula IVa: 
in which R, R2, R3 and R4 are as defined previously;
b) reaction of the compound of formula IVa with a strong base in an aprotic solvent in order to obtain an intermediate ring compound of formula Va: 
which, after elimination of a water molecule, forms a compound of general formula Ia; and
c) isolation of the compound of general formula Ia thus obtained.
Preference is particularly given to the compounds of general formula Ia in which
R represents the cyclopropylmethyl group, and
R2, R3 and R4 represent the methyl group.
In a second embodiment of the invention, the group R1 is a substituted phenyl ring.
The compound of general formula I then becomes a compound of general formula Ib: 
in which R2 is as defined previously and X is chosen from amongst:
hydrogen;
halogen;
(C1-C3) alkoxy;
CN;
(C1-C3) fluoroalkyl;
(C1-C3) alkyl;
xe2x80x94COOH.
The method of the invention then comprises the following steps:
a) reaction of a compound of general formula II 
in which R2, R3 and R4 are as defined previously and R12 represents a C1-C6 alkyl group,
with an acid of general formula III b) 
in which X is as defined previously, in an anhydrous medium, in order to form a compound of general formula IV b) 
R2, R3 and R4 being as defined above;
b) reaction of the compound of formula IVb with a strong base in an aprotic solvent in order to obtain an intermediate ring compound of formula Vb: 
which after elimination of a water molecule, forms a compound of general formula Ib; 
c) isolation of the compound of general formula Ib thus obtained.
The intermediate compound of general formula VI is novel and constitutes another object of the invention.
In particular the compounds of general formula IV in which R2, R3 and R4 represent the methyl group and R12 is as defined above are preferred.
A particularly preferred compound of this type in the one in which R12 represents methyl.
The method of the invention is illustrated by means of the following example: